16 November 2011

Color-tagged Ring-billeds in Chicago

In the spring of 2007, the City of Chicago and the USDA Wildlife Services conducted a study on two Ring-billed Gull colonies in Chicago, IL. The study was an egg-oiling project initiated by the City. The goal was to determine whether oiling eggs during the nesting season would reduce the number of gulls on local beaches. Ordinary corn oil is one way to prevent oxygen from penetrating the eggshell, thus preventing the young from ever hatching. Adult parents continue to incubate and invest energy in nesting, but to no avail. This is, as one of my friends put it "murder in a non-lethal way".  

What would be the rationale in decreasing the number of Ring-billeds on the lakefront?

The primary reason given by the City of Chicago is that fecal deposits of gulls have long been one of the causes for increased E.coli levels in near-shore waters along the lakefront. The aim was to track the movements of birds that had their eggs oiled (or not) and to determine if they would abandon their respective colonies.

During the nesting season of 2007, some gulls were part of a control group (eggs not oiled) and some were given treatments (eggs oiled). Colored wing tags (patagial tags) were attached to both wings of 724 gulls from the Dime Pier colony (approximately 3,100 nests) and the Lake Calumet colony (approximately 31,400 nests). From the Dime Pier colony, 94% of the nests were oiled (7,396 eggs) and from the Lake Calumet colony, 48% of the nests were oiled (41,753 eggs). The tags attached to the local Ring-billeds consisted of four different colors: blue, green, yellow or orange.

Adult Ring-billed. Montrose Beach. Chicago, IL; 2 November 2010.
This individual had its eggs oiled at the Dime Pier colony (directly south of Navy Pier). Photo by Amar Ayyash.

I've summarized the project's methods in the tables below:

Lake Calumet Colony

Tag Color
Blue (eggs not oiled)
Yellow (eggs oiled)
Dime Pier Colony

Tag Color
Green (eggs not oiled)
Orange (eggs oiled)

Same adult as above.  The irony of this sighting is that this bird was found just miles from where it once attempted to nest. Even more interesting is that it was found along the lakefront more than 3 years later. So technically, it could be safely aged to "at least" 6 years old.

The findings of this study were not instantaneous since subsequent hatch-year numbers had to be reviewed. Data was collected by biologists with the USDA Wildlife Services from April of 2007 through April of 2009. During this time, the public was called on to report any tagged gulls. The USDA used press releases and online announcements to garner the input of many birding organizations. Resightings were reported from some twenty different states (and one Canadian province). Unsurprisingly, many of the winter resightings came from the Gulf Coast states; this agrees with earlier studies regarding the movements of Ring-billeds on the Great Lakes (Gabrey, 1996). Also of interest to me is that no tagged RBGUs were reported in Chicago during the winter seasons. This reinforces my suspicion that Chicago Ring-billeds are replaced by a different population during the winter months.   

Resightings of tagged birds:
Tag Color
% of total tagged birds
% of total tagged birds
% of total tagged birds
Interestingly, there was approximately a 3 to 1 ratio of yellow and orange-tagged resightings over blue and green-tagged birds. Why this color bias existed is still unknown.The biologists and volunteers who conducted regular spot counts at the breeding colonies (at least twice per week) also recorded a similar color bias.  

Having reported two of these tagged gulls myself, I felt obligated to get details about this program and so I contacted the Supervisory Wildlife Biologist from the USDA, Thomas W. Seamans. It seemed odd to me that a relatively small percentage of the control group was reported, while a much, much, greater amount of resightings came from the treatment group. This struck me as backwards! Seamans admitted that "there is a problem with this marking technique [patagial tags] that could really cause a misinterpretation of data collected by biologists". He also added that "if we had been looking at long term movements then it [the tagging program] would have been a problem".

It's important to keep in mind that no hatch-year birds with wing-tags were reported during the breeding season of 2007 (nor were any reported the following year when they could still be distinguished from adults by plumage). In fact, not one tagged subadult was ever reported by the public or recorded by the Wildlife Services team throughout the entire project.

Incidentally, Steve Ambrose and I found an adult with a blue tag last weekend at Monroe Harbor in Chicago. Blue-tagged birds were part of the control group with no oiled eggs. I proudly reported this bird to Seamans and he was, as usual, very helpful in entertaining my questions. My resighting was only the eighth report this year and the fact that I found a blue tagged bird "makes for a rather rare sighting"! Naturally, as time progresses, less and less of these birds are being reported - some are losing their tags and some are perishing. 

Monroe Harbor. Chicago, IL. 12 November 2011. The tag on the right wing was missing. This individual could have been a hatch-year bird when it was tagged or an adult. The swollen left tibia and notably short legs make for a somewhat abnormal looking Ring-billed.
Over 97% of the nests with oiled eggs from the 2007 breeding season effectively failed. Nests that were not oiled did not suffer any "complete" clutch loss (Rader, 2008). One might argue that the City of Chicago was not trying to eliminate the entire population of both colonies but I would beg to differ. The only reason why a good percentage of nests were left unoiled in the Lake Calumet colony is because the City would have exceeded the Federal and State permits for the project (the City underestimated the number of nests on its permit application).  

I personally think the City acted disingenuously. Were they really interested in "understanding" the movements and/or reactions of the gull colonies during the breeding season of 2007? My feeling is that they wanted a quick fix to eradicate the RBGU numbers along the lakefront and they partially succeeded in doing that, but only temporarily. Their decision was rash, insensitive and ultimately a waste of taxpayer dollars. No gulls were tagged during the 2008 and 2009 breeding season and it seems like no follow-up was given to the "study". 

I'll leave my readers with one last thought from the Wildlife Services' report: "Negative effects on tagged individuals or response to tag color by conspecifics will contribute to biased results and, possibly, poor management decisions" (Seamans et al., 2010). 

I'd like to thank Thomas W. Seamans for all of his helpful information and feedback. Tom was very forthcoming and open about these findings.